Conventional silver salt diffusion transfer photographic film units and color diffusion transfer photographic film units can be classified roughly into a peeling type which requires a peeling stage to view images, and a non-peeling type which can dispense with the peeling stage.
The peeling type includes a type (hereinafter referred to as a "peel-apart" type) and a color diffusion transfer film unit (hereinafter referred to as a "peelable monosheet" type) as diffusion transfer photographic film units. In the peel-apart type, a sensitive layer and a dye image receiving layer are separately coated on separate supports, respectively, a sensitive element and the dye image receiving element are superposed after the exposure of an image, a processing composition is spread therebetween and the dye image receiving element is then peeled off, whereby a dye image transferred to the dye image receiving layer is obtained on the side to be peeled. In the peelable monosheet type, at least an image receiving layer, a peeling layer and a sensitive element in this order are provided on the same support and the image receiving layer is peeled off from the peeling layer after an alkaline processing composition is applied for development. Diffusion transfer photographic film units of the peelable monosheet type provides a high-quality image obtained by peeling type color diffusion film units as well as an excellent handleability of non-peeling type color diffusion film unit as well as the excellent handleability provided by non-peeling type color diffusion transfer photographic film units.
However, these types have the disadvantages that the alkaline processing solution is sticky on the surface of the image and is liable to adhere to the surrounding zones after peeling, and the used film is not convenient to handle. Further, there is the disadvantage that the peeling layer is broken when being peeled off and the broken peeling layer is randomly deposited on the surface from which the peeling layer has been peeled.
The non-peeling type include a type in which an image receiving layer and a silver halide emulsion layer are provided on the same transparent support and a type where the image receiving layer and emulsion layer are provided on separate supports, although in the non-peeling type dye image receiving layer and the silver halide emulsion layer are provided between the transparent support and the other support. In the former case, a white light reflecting layer is provided between the image receiving layer and the silver halide emulsion layer, while in the latter case, a white pigment is incorporated in a processing composition to be spread between the image receiving layer and the silver halide emulsion layer, whereby a dye image transferred to the image receiving layer can be viewed by reflected light.
However, when the used emulsion, pod, and cover sheet are left un-peeled, the resulting print is too thick. Hence, peeling them off has been proposed. These conventional techniques are described in JP-A-47-8237, JP-A-59-220727, JP-A-59-229555, JP-A-56-65133, JP-A-45-24075, JP-A-49-4653, JP-A-49-4334, U.S. Patents 3,658,524, 3,227,550 and 4,359,518. However, problems are caused since the alkaline processing solution is sticky on the surface of the image and is liable to adhere to the surroundings after peeling; the used film is not convenient to handle; and the peeling layer is broken when peeled and the broken peeling layer is randomly deposited on the surface which has been peeled.
Other problem of the peeling type color diffusion transfer photographic film unit ,including both the peel apart type and the peelable monosheet type as well as a type in which the unnecessary part of the non-peeling type can be peeled, is that sharpness is lowered, when the space between the image receiving layer and the sensitive element is increased. However, when the distance between the sensitive layer and the image receiving layer is 10 .mu.m or shorter, the problem exists that a cyan coloring material contained in the sensitive layer is dissolved in the alkaline developing solution and diffused during development and the image receiving layer is fogged.
Examples of materials for the peeling layers of the diffusion transfer photographic film unit include water-soluble or hydrophilic polymers such as gum arabic (U.S. Pat. Nos. 2,759,825 and 4,009,031), hydroxymethyl cellulose (U.S. Pat. No. 2,759,825 and JP-A-47-8237), methyl cellulose, ethyl cellulose and nitrocellulose (U.S. Pat. No. 2,759,825), cellulose acetate (Canadian Pat. No. 681,777), cellulose acetate hydrogen phthalate (Canadian Pat. No. 681,777), carboxymethylcellulose (U.K. Pat. No. 2,012,064), cellulose derivatives [JP-B-45-24075 (the term "JP-B" as used herein means an "examined Japanese patent publication")], starch ether (JP-B-50-35820), galactomannan (U.K. Pat. No. 869,190), pectin (U.S. Pat. No. 2,759,825), phthalated gelatin (JP-B-45-24075, JP-A-54-74431, JP-A-54-126535), sodium alginate (U.S. Pat. No. 2,759,825), polyvinyl alcohol (U.S. Pat. No. 2,759,825, U.K. Pat. No. 2,012,064 and JP-B-45-24075), and polymethacrylic acid (U.S. Pat. No. 2,759,825).
Further, as the materials for the peeling layer include water-insoluble synthetic polymers such as vinyl acetate-maleic anhydride copolymer and methyl methacrylate-acrylic acid copolymer (JP-B-45-15902), barbituric acid-formalin condensate (JP-B-49-4333), hydantoinformalin condensate (JP-B-49-4334), and graft copolymers of gelatin fully reacted with anhydrous dicarboxylic acid, such as phthalic anhydride, and a monomer, such as a vinyl ester, a vinyl ether or an acrylic ester, or a mixture thereof (JP-A-56-65133).
Further, there has been proposed the use of a peeling layer composed of a terpolymer of styrene with acrylic acid (or methacrylic acid) and methyl methacrylate (or methyl acrylate), the terpolymer being dispersed in a water-soluble polymer such as hydroxyethyl cellulose (U.S. Pat. No. 4,366,227).
However, the peeling layers described in these patent publications still have problems with respect to failure in long-term stability during storage, failure in the formation of films, unevenness in the formed image, a powder depositing phenomenon (the deposited processing solution is crystallized on the surface of the image and the image becomes cloudy) and insufficient peeling property.
There have been proposed a method using an acrylic acid peeling layer disclosed in JP-A-60-214357 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") and a method for providing temporarily a barrier against the alkaline processing solution in the photographic layer disclosed in JP-A-60-257446 and JP-A-60-257447. However, the coloring material in the sensitive layer is dissolved in the alkaline developing solution and diffused in the image receiving layer. Therefore, the selective diffusion of the coloring material in the image receiving layer can not be prevented, though the diffusion of the alkaline developing solution can be prevented.
However, the problem of stickiness of the surface of the image immediately after the peeling of the image receiving layer is still unsolved. There is a problem that when the surface of the image is touched with fingers immediately after peeling, fingerprints are left.
The color diffusion transfer photographic film unit has a problem that the coloring material contained in the sensitive layer is dissolved in the alkaline developing solution and diffused during development and, as a result, the image receiving layer is fogged and an image having a high minimum image density (Dmin) is obtained. As described above, when the distance between the sensitive layer and the image receiving layer is 10 .mu.m or shorter, the coloring material contained in the sensitive layer is dissolved in the alkaline developing solution and diffused during development and the image receiving layer is fogged. Increasing the film thickness between the sensitive layer and the image receiving layer to prevent diffusion, causes a lowering of sharpness.
When the film thickness is kept to 10 .mu.m or less, the coloring material cannot be prevented from being dissolved in the alkaline solution and being diffused and the scratch resistance of the image on the image receiving layer after peeling is lowered. Therefore, the surface of the image after peeling is easily damaged. Accordingly, a method is sought which solves several disadvantages.